Image sensor having wave guide and method for manufacturing the same

ABSTRACT

An image sensor having a wave guide includes a semiconductor substrate formed with a photodiode and a peripheral circuit region; an anti-reflective layer formed on the semiconductor substrate; an insulation layer formed on the anti-reflective layer; a wiring layer formed on the insulation layer and connected to the semiconductor substrate; at least one interlayer dielectric stacked on the wiring layer; and a wave guide connected to the insulation layer by passing through the interlayer dielectric and the wiring layer which are formed over the photodiode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/758,646, filed on Apr. 12, 2010, the disclosure of which isherein incorporated by reference in its entirety. The U.S. patentapplication Ser. No. 12/758,646 claims priority to Korean ApplicationNo. 10-2009-0033400 filed on Apr. 17, 2009, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image sensor having a wave guide asa traveling path of incident light and a method for manufacturing thesame, and more particularly, to an image sensor having a wave guide, inwhich a separate wiring layer is formed over a photodiode so thatetching uniformity is secured and the generation of dark current byplasma ions during an etching process is prevented when forming a waveguide through etching, and a method for manufacturing the same.

2. Description of the Related Art

Image sensors are semiconductor devices which convert an optical imageinto electrical signals. Representative image sensors include a chargecoupled device (CCD) and a CMOS image sensor.

Between these two image sensors, the CMOS image sensor stands for adevice which converts an optical image into electrical signals using aCMOS manufacturing technology. The CMOS image sensor adopts a switchingscheme in which MOS transistors are formed by the number of pixels andoutputs are sequentially detected using the CMOS transistors.

When compared to the CCD image sensor which has been widely usedheretofore as an image sensor, in the CMOS image sensor, a simpledriving scheme is used, and various scanning schemes can be realized.Further, since a signal processing circuit can be integrated in a singlechip, miniaturization of a product is made possible, and since acompatible CMOS technology is employed, the manufacturing cost can bereduced and the power consumption can be significantly decreased.

The CMOS image sensor is composed of a photodiode which detects lightand a CMOS logic circuit which converts detected light into anelectrical signal as data. In order to improve the light sensitivity ofthe image sensor, efforts have been made to increase a ratio between thearea of the photodiode and the area of the entire image sensor (that isusually called a fill factor). However, because the CMOS logic circuitcannot be omitted, difficulties necessarily exist in increasing theratio.

Under these situations, light condensing technologies have beendisclosed in the art, in which paths of light incident on points otherthan the photodiode are changed to be directed toward the photodiode soas to elevate the light sensitivity. Representative technologies includea microlens forming technology and a technology using a wave guide.

In the case where light is condensed using a microlens, as the number ofintegrated pixels increases these days, the distance between themicrolens and the photodiode disposed under the microlens increasesgradually as well. Due to this face, since a focus cannot be formed onthe photodiode, a problem is caused in that light having passed throughthe microlens cannot be effectively transferred to the photodiode.

Meanwhile, research has been directed toward the technology forproviding a wave guide in the traveling path of incident light andallowing light incident on the photodiode to pass through the waveguide, thereby minimizing the loss of incident light and suppressing acrosstalk between adjacent pixels.

FIG. 1 is a cross-sectional view illustrating a conventional imagesensor having a wave guide.

Referring to FIG. 1, it can be seen that a conventional image sensorhaving a wave guide is configured in such a way that an interlayerdielectric 16 formed over a photodiode 11 is etched and a wave guide 19is formed thereby.

However, in the conventional image sensor having a wave guide, since anamount of the interlayer dielectric 16 to be etched when forming thewave guide 19 is considerable and an etching depth is substantial,etching uniformity cannot be secured. Such non-uniformity leads to thenon-uniformity of the photodiode 11, whereby the characteristics of theimage sensor are likely to deteriorate.

Also, an amount of plasma ions needed in an etching process for formingthe wave guide 19 increases, and a portion of the plasma ions isintroduced into the photodiode 11 and serves as a factor for causing adefect in the photodiode 11, whereby the characteristics of the entireimage sensor are likely to further deteriorate.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made in an effort to solvethe problems occurring in the related art, and an object of the presentinvention is to provide an image sensor having a wave guide, in which awiring layer is formed over a photodiode such that the wiring layer canbe used as an etch stop layer in the course of forming a wave guide sothat non-uniformity in etching depth can be avoided and such that theplasma-charge ions generated in an etching process can be discharged toa semiconductor substrate so that introduction of the plasma-chargedions into the photodiode can be prevented and the generation of darkcurrent can be suppressed, and a method for manufacturing the same.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided an image sensor having a waveguide, comprising a semiconductor substrate formed with a photodiode anda peripheral circuit region; an anti-reflective layer formed on thesemiconductor substrate; an insulation layer formed on theanti-reflective layer; a wiring layer formed on the insulation layer andconnected to the semiconductor substrate; at least one interlayerdielectric stacked on the wiring layer; and a wave guide connected tothe insulation layer by passing through the interlayer dielectric andthe wiring layer which are formed over the photodiode.

In order to achieve the above object, according to another aspect of thepresent invention, there is provided a method for manufacturing an imagesensor having a wave guide, comprising the steps of (a) forming ananti-reflective layer on a semiconductor substrate which is formed witha photodiode and a peripheral circuit region; (b) forming an insulationlayer on the anti-reflective layer; (c) forming a wiring layer on theinsulation layer; (d) forming at least one interlayer dielectric on thewiring layer; (e) selectively etching the interlayer dielectric untilthe wiring layer is exposed, so as to form a wave guide over thephotodiode; and (f) selectively etching the wiring layer exposed in thestep (e) until the insulation layer formed over the photodiode isexposed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, and other features and advantages of the presentinvention will become more apparent after a reading of the followingdetailed description taken in conjunction with the drawings, in which:

FIG. 1 is a cross-sectional view illustrating a conventional imagesensor having a wave guide;

FIG. 2 is a cross-sectional view illustrating an image sensor having awave guide in accordance with an embodiment of the present invention;

FIG. 3 is a plan view illustrating the image sensor having a wave guidein accordance with the embodiment of the present invention;

FIG. 4 is a flow chart illustrating a method for manufacturing an imagesensor having a wave guide in accordance with another embodiment of thepresent invention; and

FIG. 5 is a cross-sectional view illustrating a state in whichplasma-charged ions are discharged through a wiring layer to asemiconductor substrate during a process for manufacturing the imagesensor having a wave guide according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in greater detail to preferred embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numerals will be usedthroughout the drawings and the description to refer to the same or likeparts.

FIG. 2 is a cross-sectional view illustrating an image sensor having awave guide in accordance with an embodiment of the present invention.

Referring to FIG. 2, an image sensor 200 having a wave guide inaccordance with an embodiment of the present invention includes asemiconductor substrate 20, an anti-reflective layer 22, an insulationlayer 22-1, a wiring layer 25, an interlayer dielectric 26, and a waveguide 29.

A photodiode 21 and a peripheral circuit region are formed in thesemiconductor substrate 20. Since the photodiode 21 and the peripheralcircuit region formed in the semiconductor substrate 20 are the same asthose of the conventional CMOS image sensor, detailed descriptionthereof will be omitted herein.

The anti-reflective layer 22 is formed on the semiconductor substrate20, the insulation layer 22-1 is formed on the anti-reflective layer 22,and the wiring layer 25 is formed on the insulation layer 22-1. It ispreferred that the wiring layer 25 be formed of a material such astungsten (W), aluminum (Al), titanium (Ti) and silicon nitride (SiN).

The wiring layer 25 is connected to a well 24 which is formed in thesemiconductor substrate 20. In the case where the semiconductorsubstrate 20 is a P type substrate, the well 24 is formed through N+/Pjunction, and in the case where the semiconductor substrate 20 is an Ntype substrate, the well 24 is formed through P+/N junction.

At least one interlayer dielectric 26 is stacked on the wiring layer 25,and preferably, a passivation layer 27 is further formed on theuppermost interlayer dielectric 26. The wave guide 29 is formed throughthe wiring layer 25, the interlayer dielectric 26 and the passivationlayer 27 until it reaches the insulation layer 22-1 which is formed overthe photodiode 21.

A color filter is formed on the passivation layer 27 through which thewave guide 29 passes, and a microlens 28 is formed on the color filterso that light condensing efficiency is improved.

As shown in FIG. 2, in the image sensor 200 having a wave guide inaccordance with the embodiment of the present invention, after lighthaving passed through the microlens 28 and the color filter is incidenton the wave guide 29, the incident light is totally reflected in thewave guide 29 by the substance contained in the wave guide 29, and istransferred to the photodiode 21 while the loss of the incident light isminimized.

Due to the fact that the wiring layer 25 is connected to the well 24, alarge amount of plasma-charged ions, which are produced in the course offorming the wave guide 29, are not introduced into the photodiode 21 andare discharged to the semiconductor substrate 20 through the well 24,whereby advantages are provided in that the characteristics of thephotodiode 21 can be improved.

FIG. 3 is a plan view illustrating the image sensor having a wave guidein accordance with the embodiment of the present invention.

Referring to FIG. 3, in the image sensor 200 having a wave guide inaccordance with the embodiment of the present invention, it can be seenthat the wiring layer 25 including an opening for the wave guide 29 isformed over the photodiode 21 and is connected to the lower N+/P type orP+/N type well which is formed in the semiconductor substrate 20.

FIG. 4 is a flow chart illustrating a method for manufacturing an imagesensor having a wave guide in accordance with another embodiment of thepresent invention.

Referring to FIG. 4, a method for manufacturing an image sensor having awave guide in accordance with another embodiment of the presentinvention includes an anti-reflective layer forming step S410, aninsulation layer forming step S420, a wiring layer forming step S430, aninterlayer dielectric forming step S440, an interlayer dielectricetching step S450, and a wiring layer etching step S460.

In the anti-reflective layer forming step S410, the anti-reflectivelayer 22 is formed on the semiconductor substrate 20 which is formedwith the photodiode 21 and the peripheral circuit region. Then, theinsulation layer 22-1 is formed on the anti-reflective layer 22 for aninsulation purpose (S420).

In the wiring layer forming step S430, the wiring layer 25 is formed onthe insulation layer 22-1. The wiring layer 25 is connected to the well24 which is formed in the semiconductor substrate 20, so that the largeamount of plasma-charged ions produced in the process of forming thewave guide 29 are not introduced into the photodiode 21 and aredischarged to the semiconductor substrate 20 through the well 24.

In the interlayer dielectric forming step S440, at least one interlayerdielectric 26 is formed on the wiring layer 25. Preferably, thepassivation layer 27 is formed on the uppermost interlayer dielectric26.

In the interlayer dielectric etching step S450, in order to form thewave guide 29 over the photodiode 21, the interlayer dielectric 26 andthe passivation layer 27 are selectively etched.

Thereupon, the wiring layer etching step S460 is conducted, in which thewiring layer 25 exposed in the interlayer dielectric etching step S450is selectively etched until the insulation layer 22-1 formed over thephotodiode 21 is exposed.

After the opening for the wave guide 29 is defined, preferably, steps offorming the color filter and the microlens 28 on the passivation layer27 are conducted.

Meanwhile, by selectively etching a portion of the insulation layer 22-1exposed in the wiring layer etching step S460 as the occasion demands,the loss of light incident on the photodiode 21 can be further reduced.

An essential idea of the present invention resides in that a wiringlayer is formed in advance over a photodiode before forming a waveguide, in such a way as to be connected to a well of N+/P type or P+/Ntype, so that the plasma-charged ions produced in a process of formingthe wave guide are discharged to a semiconductor substrate through thewell of N+/P type or P+/N type, thereby preventing the plasma-chargedions from being introduced into the photodiode.

As the wiring layer formed in advance over the photodiode serves as anetch stop layer in a process of forming the wave guide, it is possibleto etch the wave guide formed over the photodiode to have a uniform opendepth. Thereafter, as the wiring layer having served as the etch stoplayer is etched to define the wave guide, an opening procedure forforming the wave guide is completed.

That is to say, after the opening procedure is conducted for aninterlayer dielectric through etching until the wiring layer is exposed,by further opening the wiring layer having served as the etch stoplayer, the opening procedure for the formation of the wave guide iscompleted.

FIG. 5 is a cross-sectional view illustrating a state in whichplasma-charged ions are discharged through a wiring layer to asemiconductor substrate during a process for manufacturing the imagesensor having a wave guide according to the present invention.

Referring to FIG. 5, it can be seen that the plasma-charged ionsproduced in the procedure of opening a wave guide are not introducedinto a photodiode 31 and are discharged to a semiconductor substrate 30through a well 34 of N+/P type or P+/N type.

As is apparent from the above description, the image sensor having awave guide and the method for manufacturing the same according to thepresent invention provide advantages in that, since a wiring layer isformed over a photodiode and is used as an etch stop layer in the courseof forming a wave guide, non-uniformity in etching depth can be avoidedand due to this fact, the imaging characteristics of the photodiode canbe improved.

Also, since the plasma-charged ions used in an etching process aredischarged to a semiconductor substrate through a wiring layer, theintroduction of a source which is likely to cause a defect in thephotodiode can be prevented, whereby generation of dark current can besuppressed.

Although preferred embodiments of the present invention have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and the spirit of theinvention as disclosed in the accompanying claims.

What is claimed is:
 1. A method for manufacturing an image sensor havinga wave guide, comprising the steps of: (a) forming an anti-reflectivelayer on a semiconductor substrate which is formed with a photodiode anda peripheral circuit region; (b) forming an insulation layer on theanti-reflective layer; (c) forming a conductive wiring layer on theinsulation layer; (d) forming at least one interlayer dielectric on thewiring layer; (e) selectively etching the interlayer dielectric untilthe wiring layer, is exposed, so as to form a wave guide over thephotodiode; and (f) selectively etching the wiring layer exposed in thestep (e) until a portion of the insulation layer formed over thephotodiode is exposed; wherein the wiring layer provides a conductorthat allows plasma-charged ions in the wave guide to be discharged intothe semiconductor substrate and not be introduced into the photodiode.2. The method according to claim 1, wherein the step (c) comprises thestep of: (c1) connecting the wiring layer to a well which is formed inthe semiconductor substrate.
 3. The method according to claim 2, whereinthe step (d) comprises the step of: (d1) forming a passivation layer onan uppermost interlayer dielectric.
 4. The method according to claim 2,wherein the well is formed through N+/P junction when the semiconductorsubstrate is a P type substrate, and is formed through P+/N junctionwhen the semiconductor substrate is an N type substrate.
 5. The methodaccording to claim 2, wherein, in the step (c), the wiring layer isformed using tungsten (W), aluminum (Al), or titanium (Ti).
 6. Themethod according to claim 2, further comprising the step of: (g) etchinga portion of the insulation layer exposed in the wiring layer etchingstep.
 7. The method according to claim 2, further comprising the stepsof: (h) forming a color filter on the passivation layer; and (i) forminga microlens on the color filter.
 8. The method according to claim 1,wherein the wiring layer acts as a etch stop layer in the course offorming a wave guide so that non-uniformity in etching depth can beavoided.
 9. The method according to claim 2, wherein the wiring layerallows plasma-charged ions in the wave guide to be discharged into thesemiconductor substrate via the well formed in the semiconductorsubstrate.